Add support for null literals

Author: Mike

definition.go

@@ -158,6 +158,9 @@ func GetNullable(ttype Type) Nullable {
 	return ttype
 }
 
+// NullValue to be able to detect if a value is set to null or if it is omitted
+type NullValue struct {}
+
 // Named interface for types that do not include modifiers like List or NonNull.
 type Named interface {
 	String() string

language/ast/node.go

@@ -22,6 +22,7 @@ var _ Node = (*IntValue)(nil)
 var _ Node = (*FloatValue)(nil)
 var _ Node = (*StringValue)(nil)
 var _ Node = (*BooleanValue)(nil)
+var _ Node = (*NullValue)(nil)
 var _ Node = (*EnumValue)(nil)
 var _ Node = (*ListValue)(nil)
 var _ Node = (*ObjectValue)(nil)

language/ast/values.go

@@ -16,6 +16,7 @@ var _ Value = (*IntValue)(nil)
 var _ Value = (*FloatValue)(nil)
 var _ Value = (*StringValue)(nil)
 var _ Value = (*BooleanValue)(nil)
+var _ Value = (*NullValue)(nil)
 var _ Value = (*EnumValue)(nil)
 var _ Value = (*ListValue)(nil)
 var _ Value = (*ObjectValue)(nil)
@@ -172,6 +173,34 @@ func (v *BooleanValue) GetValue() interface{} {
 	return v.Value
 }
 
+// NullValue implements Node, Value
+type NullValue struct {
+	Kind  string
+	Loc   *Location
+	Value interface{}
+}
+
+func NewNullValue(v *NullValue) *NullValue {
+
+	return &NullValue{
+		Kind:  kinds.NullValue,
+		Loc:   v.Loc,
+		Value: v.Value,
+	}
+}
+
+func (v *NullValue) GetKind() string {
+	return v.Kind
+}
+
+func (v *NullValue) GetLoc() *Location {
+	return v.Loc
+}
+
+func (v *NullValue) GetValue() interface{} {
+	return nil
+}
+
 // EnumValue implements Node, Value
 type EnumValue struct {
 	Kind  string

language/kinds/kinds.go

@@ -23,6 +23,7 @@ const (
 	FloatValue   = "FloatValue"
 	StringValue  = "StringValue"
 	BooleanValue = "BooleanValue"
+	NullValue	 = "NullValue"
 	EnumValue    = "EnumValue"
 	ListValue    = "ListValue"
 	ObjectValue  = "ObjectValue"

language/parser/parser.go

@@ -610,7 +610,15 @@ func parseValueLiteral(parser *Parser, isConst bool) (ast.Value, error) {
 				Value: value,
 				Loc:   loc(parser, token.Start),
 			}), nil
-		} else if token.Value != "null" {
+		} else if token.Value == "null" {
+			if err := advance(parser); err != nil {
+				return nil, err
+			}
+			return ast.NewNullValue(&ast.NullValue{
+				Value: nil,
+				Loc:   loc(parser, token.Start),
+			}), nil
+		} else {
 			if err := advance(parser); err != nil {
 				return nil, err
 			}

language/parser/parser_test.go

@@ -183,15 +183,6 @@ func TestDoesNotAcceptFragmentsSpreadOfOn(t *testing.T) {
 	testErrorMessage(t, test)
 }
 
-func TestDoesNotAllowNullAsValue(t *testing.T) {
-	test := errorMessageTest{
-		`{ fieldWithNullableStringInput(input: null) }'`,
-		`Syntax Error GraphQL (1:39) Unexpected Name "null"`,
-		false,
-	}
-	testErrorMessage(t, test)
-}
-
 func TestParsesMultiByteCharacters_Unicode(t *testing.T) {
 
 	doc := `
@@ -367,6 +358,7 @@ func TestAllowsNonKeywordsAnywhereNameIsAllowed(t *testing.T) {
 		"subscription",
 		"true",
 		"false",
+		"null",
 	}
 	for _, keyword := range nonKeywords {
 		fragmentName := keyword

language/printer/printer.go

@@ -367,6 +367,15 @@ var printDocASTReducer = map[string]visitor.VisitFunc{
 		}
 		return visitor.ActionNoChange, nil
 	},
+	"NullValue": func(p visitor.VisitFuncParams) (string, interface{}) {
+		switch node := p.Node.(type) {
+		case *ast.NullValue:
+			return visitor.ActionUpdate, fmt.Sprintf("%v", node.Value)
+		case map[string]interface{}:
+			return visitor.ActionUpdate, getMapValueString(node, "Value")
+		}
+		return visitor.ActionNoChange, nil
+	},
 	"EnumValue": func(p visitor.VisitFuncParams) (string, interface{}) {
 		switch node := p.Node.(type) {
 		case *ast.EnumValue:

rules.go

@@ -1730,6 +1730,12 @@ func isValidLiteralValue(ttype Input, valueAST ast.Value) (bool, []string) {
 			return true, nil
 		}
 
+		// This function only tests literals, and assumes variables will provide
+		// values of the correct type.
+		if valueAST.GetKind() == kinds.NullValue {
+			return true, nil
+		}
+
 		// This function only tests literals, and assumes variables will provide
 		// values of the correct type.
 		if valueAST.GetKind() == kinds.Variable {

scalars.go

@@ -162,6 +162,8 @@ var Int = NewScalar(ScalarConfig{
 			if intValue, err := strconv.Atoi(valueAST.Value); err == nil {
 				return intValue
 			}
+		case *ast.NullValue:
+			return NullValue{}
 		}
 		return nil
 	},
@@ -299,6 +301,8 @@ var Float = NewScalar(ScalarConfig{
 			if floatValue, err := strconv.ParseFloat(valueAST.Value, 64); err == nil {
 				return floatValue
 			}
+		case *ast.NullValue:
+			return NullValue{}
 		}
 		return nil
 	},
@@ -326,7 +330,10 @@ var String = NewScalar(ScalarConfig{
 		switch valueAST := valueAST.(type) {
 		case *ast.StringValue:
 			return valueAST.Value
+		case *ast.NullValue:
+			return NullValue{}
 		}
+
 		return nil
 	},
 })
@@ -485,6 +492,8 @@ var Boolean = NewScalar(ScalarConfig{
 		switch valueAST := valueAST.(type) {
 		case *ast.BooleanValue:
 			return valueAST.Value
+		case *ast.NullValue:
+			return NullValue{}
 		}
 		return nil
 	},
@@ -506,6 +515,8 @@ var ID = NewScalar(ScalarConfig{
 			return valueAST.Value
 		case *ast.StringValue:
 			return valueAST.Value
+		case *ast.NullValue:
+			return NullValue{}
 		}
 		return nil
 	},
@@ -564,6 +575,9 @@ var DateTime = NewScalar(ScalarConfig{
 		switch valueAST := valueAST.(type) {
 		case *ast.StringValue:
 			return unserializeDateTime(valueAST.Value)
+			return valueAST.Value
+		case *ast.NullValue:
+			return NullValue{}
 		}
 		return nil
 	},